Basic threading

It is said that the Greeks invented the screw back in the 5th century BC. The Romans invented the first screws for going into wood. These were made of bronze and silver and the threads were made by filling them, or by soldering a wire that had been wound in a spiral.

 

The first written reference to a screw was in the early 1400´s. Leonardo Da Vinci’s designs from around the same time (the late 1400’s) for machines that could cut screws apparently passed unnoticed, because the first machine of this type was built in 1568 by a French mathematician, Jaques Besson.

The first nuts and bolts appeared in the middle 1400´s. The bolts were just screws with straight sides and a blunt end. The nuts were handmade and very crude. When a match was found between a nut and a bolt, they where kept together until they were applied in an industrious manner.

 

Sir Joseph Whitworth (1803~1887), an English mechanical engineer and inventor was born in Stockport in 1803. At the age of fourteen he became an apprentice to a cotton-spinner in Derbyshire. In 1821 he moved to Manchester where he found work as a mechanic. In 1833 he set up his own machine shop.

 

[In the nineteenth century, most factories that needed a fastener would device their own system. Clearly this resulted in all sorts of compatibility problems.

 

Sir Joseph Whitworth was early impressed with the idea that if it were possible for all engineers to use the same sized taps and dies, not only a very great saving would be effected, but all work would be much better done. He therefore made a collection of all the screw threads of the different firms in England, and in 1841 he devised a standardized threading system which was a compromise of them all.

 

The system was at once adopted by the railways, and very soon became a universal standard – British Standard Whitworth (BSW). The Whitworth thread form was based on a 55 degree thread angle and rounded roots and crests.

 

Twenty years later in America a thread form called the Sellers form was introduced, as the US Standard later to be known as the American National Coarse (A.N.C) and National fine (N.F) threads. The Sellers thread used a thread angle of 60 degrees and flattened roots and crests.